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thermochromic
thermally induced reactions and relationship between
chemical changes and heat.
thermochromic LO technology in which appearance is
changed by variation in temperature.
thermochromic tube CRT with phosphor replaced by
heat-sensitive layer.
thermocline Sharp submarine temperature gradient.
thermocouple Instrument based on Seebeck effect
which measures temperature difference between pair of
dissimilar-metal junctions; much used for hightemperature
measures using refractory metals, and in
common copper/constantan junction at room temperature,
eg for met. observation.
thermodynamics Science based upon heat flow and
temperature changes, esp. those in moving fluids.
thermodynamic cycle Operating cycle of any heat
engine. In some, eg virtually all piston engines, one parcel
of fluid at a time goes through complete ** in same
enclosed (usually variable-size) volume; in others, eg gas
turbines, continuous flow of fluid goes through ** by
passing from one part of device to another, each component
handling only one part of **. The working fluid
may be recycled, continually changing state liquid/
vapour.
thermodynamic efficiency See thermal efficiency.
thermodynamic energy equations Exact expressions of
variation of pressure, volume and temperature in
reversible processes in perfect gas.
thermodynamic equilibrium Time-invariant state in
which all processes are balanced by reverse process and
entropy production vanishes.
thermoelectric cooling Local cooling using Peltier and
cooling ‘hot’ junction; ‘cold’ junction then falls to desired
level at -20 to -30°C.
thermoelectric generator Electric generator based on
thermocouples using Seebeck, Thompson, Kelvin or
Peltier effects; common spacecraft systems use nuclear
reactor or radio-isotope to heat junction often based on
Ge/Si alloy.
thermogram 1 Single-line output of traditional thermograph.
2 Pictorial output of thermographic camera.
thermograph Recording thermometer using pen/chart
or light-spot trace on film. Output is a thermogram.
thermographic camera IR camera, usually of IRLS type.
thermography Translation of temperature changes in a
scanned scene into visual picture, today important in military
and civil aerial reconnaissance, industrial process
control, medicine and many other fields. Either
black/white (black = cold, white = hot) or colour.
thermohydrometer Hydrometer with thermometer,
giving two chart outputs.
thermometer Instrument for measuring temperature.
thermometer screen Louvred box screening
thermometer from direct sunlight; usually contains other
met. instruments and in US called instrument shelter.
thermonuclear Processes in which extremely high
temperatures are used to initiate fusion of light nuclei.
thermonuclear weapon Hydrogen bomb.
thermopile Thermoelectric generator comprising stack
of thermocouples.
thermoplastic recording Patented (GE) process for
recording sound or video signals via electron beam direct
thin-film circuit
on thermoplastic layer heated by microscopic currents
induced in underlying conductive layer.
thermoplastics Large class of synthetic polymers which
may be repeatedly softened and remoulded by heating.
thermosetting plastics Synthetic polymers that are chemically
changed irreversibly by chemical action, for
example a hardening agent, or by EM radiation, notably
heat or UV irradiation, generally setting hard.
thermosphere Outermost region of atmosphere from top
of mesosphere outwards into space, characterized by
more or less steadily increasing temperature with distance
from Earth.
thermostat Device for maintaining a desired temperature
by taking action at preset limits of low and high
temperature.
thermotropic model Atmosphere used in forecasting one
temperature and one pressure surface.
Thesh Threshold, also Thld, THR.
theta Greek letter θ, used for many parameters,
including pitch angle (thus, θ = pitch rate) and azimuth
(hence Rθ). See Appendix 1.
THI Tactical hit indicator.
thickened fuel Aircraft fuel designed to resist fine dispersion
and instead to break down in crash into globules
with near-zero surrounding vapour; generally synonymous
with gelled fuel.
thick-film Very diverse technology of electronics
involving processing, high-current devices, currentgeneration
(inc. solar cells) and many other topics, mainly
using insulating substrates but often with semiconductor
layer.
thickness 1 Of wing, maximum straight-line distance
from external skin of upper surface to external skin of
lower surface measured in plane of aerofoil profile and
perpendicular to chord line.
2 According to some authorities, measured perpendicular
to camber line.
thickness/chord Ratio of thickness to chord of wing,
both measured in plane of aerofoil profile at same station.
thickness distance Distance aft of leading edge of
maximum thickness of supersonic rhomboidal or doublewedge
wing, expressed as % chord.
thickness gauge See feeler gauge.
thickness lines Lines joining points on chart where
vertical distance between pressure surfaces is everywhere
same.
thickness ratio Wing t/c ratio.
thimble 1 Pear-shaped eye around which end of control
cable is spliced.
2 Ratchet turning knob of hand micrometer.
3 Pimple-like radome, especially on or under nose
[usually adjective].
thin-aerofoil theory For most modern transonic aerofoils
t/c is low enough for it to be assumed that thickness
along the camber line is zero.
thin-case bomb Conventional bomb for blast effect
against soft target. Also called light-case (UK, WW2).
thindown Progressive energy loss by primary cosmic
rays in ionising surrounding medium.
thin-film circuit Electrical or electronic circuit formed by
depositing thin film on (usually insulating) substrate;
normal manufacturing methods are vacuum deposition
and cathode sputtering. Films may be conductive, semiconductor
or insulating.
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